Filament fob incandescent lamps



Patented Mar. 1, 1938 PATENT OFFICE 2,109,762 FILAMENT son INOANDESCENTLAMPS Shiro Abe, Nada-kn, Kobe, Kazuo Setoguchi, Motoyama-mura,'Muko-gun, Hyogo-ken, and Toyota Nagai, Suma-ku, Kobe, Japan, assign' orsto Kabushiki Kaisha Kawanisbi Kikal Seisakujo, Hayashida-ku, Kobe,Japan, a corporation of Japan No Drawing. Application September 4, 1935,Serial No. 39,138. In Japan July 6, 1935 4 Claims.

The present invention relates to improvements in a. tungsten filamentfor incandescent lampsand a method of manufacturing or producing thesame, its object being to prevent especially the sagging and twisting ofthe known filament of this kind. In the known method of manufacturing aso-called non-sagging and non-oilsetting filament, tungsten particlesare mixed with non-metallic substances, for example, silica. In such amethod, it is unknown whether said non-metallic substances really serveto prevent the over-production of the nuclei of crystals and consequent-1y produce a filament of large crystal size or reversely these impurematters hinder the growth of the crystals themselves to produce afilament of small crystal size, but it may at least be supposed thatsuch impure matters somewhat cause the lack of homogeneity in thearrangement of the molecules of the tungsten in the slug. Therefore,although the growth of the crystals may be expected by the stressproduced by the lack of the homogeneity due to said impure matters, onthe other hand it may also be expected that such stress will effect achange during recrystalliza tion. That is to say, according to anexperiment the non-sagging filaments produced by such an operationalmost without exception produce socalled twist. This phenomenon isespecially remarkable in a filament for low wattage lamps, bringingabout the pitch-short of the coil and sometimes making itunfit for itspurpose all the more because of its being non-sagging. It is consideredthat this is due to the fact that the stress is too great for the sizeof the filament and that of the nuclei of crystals must be limited.Acco'rd-' ingly, in the manufacture of a tungsten slug it is veryimportant to give it a comparatively coarse grain structure and althoughcrystals of uniform grains may be obtained by adding tungsten metalparticles of various sizes, a slug of crystals of coarse grains cannotbe obtained in this manner. Now, according to the present invention theabove-mentioned disadvantages are removed by the manufacture of a slughaving a coarse grain structure on an industrial scale andthus produce afilament which does not sag. This invention in brief is characterized bymixing one or more kinds of pure tungsten metal particles of differentsizes with one or more kinds of seasoned tungsten particles.

The seasoned tungsten particles are the pure tungsten particles leftalone at a certain temperature for a certain time in a closed vesselwith suitable humidity and are clearly different from the common puretungsten metal particles in the property, some being coated with a loweroxide film or having merely absorbed moisture or water. For example,they have their so-called cubic weight increased by about and arereduced to pure tungsten metal particles by hydrogen at approximately1,200 0., when some increase in the size of the particles is usuallyrecognized. Moreover, the operation of forming them into a slug bycompression is not only easy, but also they perform a noteworthy actionas follows. That is to say, if purse tungsten metal particles andseasoned tungsten particles are mixed together in any desiredproportion, formed into a slug by compression, and heated at sinteringtemperature, the seasoned tungsten particles are not only reduced at theabove temperature (1,200 C.) which is a low temperature during theoperation, to pure tungsten metal particles of much greater size thanthe above pure tungsten metal particleabut also when the reducedseasoned tungsten particles reach the recrystallization temperature,they-will act -as-the nuclei of crystals and annex the adjacent smallparticles of pure tungsten metal thereto to form a slug of crystals ofcoarse grain.

It is known that if a tungsten slug of coarse grain is drawn to a wireby hammering and drawing, it is possible to obtain a filament which doesnot sag, whereas the filament drawn to a wire from pure tungsten slugaccording to the present method has the advantage of hardly producingtwist, probably because the absence of impure matters tends to create ahomogeneous arrangement of the molecules of tungsten in the slug.Generally, a slug having a coarse grain structure is somewhat dimcult tobe drawn to a wire, but the inventors have succeeded in removing suchadisadvantage by performing some additional operatlons in carryin outthis invention into practice. Accordingto the inventors experiment,suitable seasoned tungsten particles are obtained by leaving alone puretungsten metal particles at atmospheric temperature for 240 hours in aclosed vessel having a humidity of about 80-90% and the quantity of saidseasoned particles to be mixed with pure tungstenmetal particles is V2to M; of the latter and may be regulated according to the requirementregarding the size of crystal grains for the thickness of the finishedfilament, etc.

For the purpose of comparing the deformations caused by the heating of afilament (A) made by mixing difierent batches of tungsten metalparticles, a filament (B) manufactured by the present method and afilament (C) made especially with the object of preventing oflset, eachof these filaments was wound into a coil and was suspendedperpendicularly with one end free and then was electrically charged atvarious voltages and heated, when it was found that under the samecondition the sag is the greatest in (C) about half as great in (A) andthe least in (B).

Having thus described our invention, claim:-

1. The method of producing a substantially non-sagging andnon-twistingfilament for incandescent lamps which consists in mixingpure tungsten metal particles with tungsten particles coated with lowertungsten oxide film, sintering the mixture into an ingot andsimultaneously reducing said oxide-coated particles to large puretungsten metal particles, and then working the pure tungsten ingot intothe form of a filament.

2. The method of producing a substantially non-sagging and non-twistingfilament for incandescent lamps which consists in mixing pure tungstenmetal particles of different sizes with tungsten particles coated withlower tungsten oxide film, the ratio of the mixture being two to fourparts by weight of pure tungsten to one part of oxide-coated tungsten,sintering the mixture into an ingot and simultaneously reducing saidoxide-coated tungsten particles to pure tungsten metal particles, andworking the pure tungsten ingot into the form of a filament.

3. The method of producing a substantially non-sagging and non-twistingfilament for incandescent lamps which consists in mixing pure tungstenmetal particles of diflerent sizes with tungsten particles coated withlower tungsten oxide film, sintering the mixture into an ingot andsimultaneously reducing said oxide-coated tungsten particles to puretungsten metal particles of enlarged size, subjecting the ingot to arecrystallization temperature to form the reduced oxidecoated'tungstenparticles as the nuclei of crystals annexing adjacent small particles ofpure tungsten to form an ingot of coarse grain, and subsequentlyhammering and drawing the tungsten ingot thereby to work the same intothe form of a filament.

4. The method of producing a substantially non-sagging andVnon-twlstingfilament for incandescent lamps which consists in subjecting particlesof tungsten to humidity in a closed ves-.

sel thereby to coat said particles with lower tung-

